The catalytic site thiol-containing tryptic peptide of bovine liver UDP-D-glucose dehydrogenase (BL UDPGDH) will be sequenced by the Edman-dansyl technique. Subsequently the sequence of the analogous peptide from Escherichia coli UDP-D-glucose dehydrogenase will be determined. Amino acid analysis of BL-UDPGDH inactivated by butanedione (BDO) treatment will establish the relationship between arginyl moieties and catalytic activity. BDO-treated BL-UDPGDH, previously labeled at the catalytic site thiols will be subjected to tryptic digestion and the sequence of the resultant peptides which contain the catalytic site sulfhydryl will be determined.